If your truly interested in Naval History, regarding flags, you should heed the advise given, on the maritime museums or visit the Naval History Center at the Washington Naval Yard. However, if it is just the one flag that you wish to research, search for invoices or pay records for the yards at Mobile Bay or the river during this period, the Naval History Center may be of help. I cataloged several references to Mobile ship builders, maybe my replacement could dig into those files for you.

Jasper